Under the direction of the writer, comparison of the records of crimes of violence with the weather records, by officials of the U. S. Weather Bureau, showed a marked increase of crime of this sort during midsummer as against midwinter, and the extremely hot summer showed more crime than the cool ones. During recent years Ellsworth Huntington has made exhaustive and extremely valuable studies of the records of piece workers in factories and elsewhere from New England and the Middle Atlantic States down to Florida and the Gulf of Mexico, and also of the mental activities of the cadets at West Point and Annapolis, and of the students in colleges, as shown by their recitation markings.[4] He has compared these records with the weather day by day and hour by hour and definitely shown a direct relation between variations in the meteorological conditions and human efficiency. He finds that people’s health and strength are greatest when the temperature falls to between 56° and 60° at night and rises to somewhere between 68° and 72° during the day. He has determined the optimum, or, in other words, the meteorological conditions best suited to man’s health, happiness, and efficiency. For mental activity the optimum temperature is much lower than for physical. People’s minds are more alert, they reason with greater analytic precision, they have greater confidence in their decisions and they are more optimistic, when the temperature falls to about freezing at night and rises to 45° or 50° during the day. Except for limited activities, the most efficient man is the one in whom the mental and physical faculties are most perfectly coördinated. Broadly speaking, this agreement may be best accomplished during times when the daily temperature ranges between 45° and 65°. Excessive humidity in midsummer—eighty per cent. or over—is harmful and adds enormously to the death rate; on the other hand, some of the worst colds may come from extreme dryness in summer. It may be found feasible to dry the air in sleeping and living rooms in summer when the humidity is too high, by closing the apartment and forcing the air over or through calcium carbide or melting ice and salt. When the air is kept at 65 to 70 per cent. humidity in winter one will feel comfortable in a much lower temperature—about 68°—than when the air is extremely dry, as it usually is in the average living apartment. With a relative humidity of 30 to 40 per cent. which one now often finds in warm houses in winter, the temperature may be forced up to 75° or over and still one may feel cold, because of the rapid evaporation from the pores of the skin, and the cold created inside the clothing by the heat lost in the process of evaporation. Bear in mind that perspiration is going on at all temperatures, even if one is unconscious of the fact.